During metal recycling, such as recycling aluminum (including aluminum alloys), organic coatings, such as paints, lacquers, and the like must be removed. Metal scrap can be crushed, shredded, or chopped into smaller pieces. The smaller pieces are then decoated, melted, and recovered.
Decoating is an important step that prevents violent gas evolution during melting. In concurrent decoating kilns, the process gas can become saturated with pyrolysis gases, rendering the decoating process difficult to control and leading to poor decoating. Existing decoating kilns may leave residual carbon residue on the scrap material, which can decrease the efficiency of post-decoating processes, including melting.
In concurrent decoating kilns, the percentage of free oxygen at the entry side of the kiln can begin relatively high and slowly decrease as pyrolysis gases build up. Concurrent decoating kilns are not capable of providing a higher oxygen level at the exit end of the kiln than the entry level of the kiln. Since good decoating requires free oxygen during the final stages, concurrent decoating kilns rely upon higher free oxygen content at the entry end. In some cases, the free oxygen is fully consumed in the kiln and decoating in the final stages is compromised. In other cases, the large amounts of free oxygen left in the mixed gases can allow the mixture to ignite and overheat components, such as when sent through the exhaust ductwork, fans, or other parts.